The Black Friday fight is on with the announcement Tuesday that Macy's will open stores at 6 p.m. on Thanksgiving, two hours earlier than last year.

Macy's is the first major retailer to announce store hours for the Black Friday weekend, often seen as the kickoff to the holiday shopping season. Last year marked the first time the department store opened its doors at 8 p.m., after opening at midnight in the several years before.

The company said the earlier opening is "in response to the significant, sustained customer interest in last year's opening on Thanksgiving."

Most stores will remain open until 10 p.m. on Black Friday, spokeswoman Holly Thomas says.

Macy's also said the majority of the Thanksgiving Day shifts have already been filled voluntarily by employees. As retailers have opened stores earlier and earlier on the holiday each year in response to shopper demand, they've received backlash from employees and customers alike for infringing on the family holiday. Yet several petitions against stores' holiday hours in recent years have failed to change retailers' strategies.

"Consumers have started to accept that shopping on Thanksgiving is a growing habit," he says. "With consumer acceptance comes more people shopping."

What used to be a one-day shopping event the day after Thanksgiving has turned into a practically week-long retail showdown as stores compete for customers during the biggest shopping period of the year. And with a shorter shopping season this year – there are 28 days from Thanksgiving to Christmas Eve – a couple more hours of shopping could be a significant boost to store sales, Osburn says.

Retailers have been pushing operating hours into Thanksgiving since Toys R Us decided to open at 9 p.m. on the holiday in 2011. Last year, Kmart (SHLD) was the most extreme, opening doors at 6 a.m. on Thanksgiving and remaining open until 11 p.m. on Black Friday.

Target (TGT), Kohl's (KSS) and J.C. Penney (JCP) all opened at 8 p.m. last year. While those retailers may likely follow Macy's lead this year, Osburn says the extent of the store-hour creep will probably be contained to the late afternoon in coming years.

"Macy's owns Thanksgiving morning with their parade," he says. "I think they have a vested interest to keep people at home ... but each year it does seem to creep more and more into earlier in the day."